In recent years, a high-sensitivity camera capable of performing color imaging with visible light of an object under a low-illuminance environment has been developed.
However, even when such a high-sensitivity camera is used, it is not possible to perform color imaging with visible light of an object under an extremely-low-illuminance environment where visible light is almost absent, for example, at night, or under a completely dark environment where visible light is absent, that is, under a 0 lux environment.
Meanwhile, in imaging an object under such an extremely-low-illuminance environment or 0 lux environment, normally, an infrared camera is used, but in this case, since color information is not obtained, monochrome imaging is performed.
Realization of an image sensor capable of performing color imaging of an object under an extremely-low-illuminance environment or 0 lux environment such as an in-vehicle camera capable of clearly reading a mark color or the like, or a security camera capable of distinctly reading a color of clothes of a suspicious person, even in the middle of night, is desired.
On the other hand, a color signal processing circuit has been proposed (for example, see PTL 1). The color signal processing circuit acquires a color signal and an infrared signal output from a color image sensor that includes plural color component photoelectric conversion elements that are respectively provided with color filters that respectively transmit different color components on a light receiving surface thereof and receive incident light to selectively output color signals corresponding to intensities of the different color components, and an infrared component photoelectric conversion element that is provided with an infrared component transmission filter that transmits an infrared component on a light receiving surface thereof and selectively outputs an infrared signal for correcting an infrared component included in at least one of the plural color signals. The color signal processing circuit controls at least two signal gains in the color signals based on the infrared signal in order to perform adjustment of white balance of the color signals.
Further, an image input device has been proposed (for example, see PTL 2). The image input device includes a solid-state image sensor that includes plural pixels that receive visible light and infrared light from an object and convert the visible light and the infrared light into a visible light signal and an infrared light signal, respectively, storage means for storing correction data including a correction value for each pixel of the solid-state image sensor with respect to the visible light signal, correction means for correcting the visible light signal output from the solid-state image sensor based on the correction data stored in the storage means, and formation means for calculating chrominance information from the corrected visible light signal and calculating luminance information from the corrected visible light signal and the infrared light signal to form a color image signal, in which the correction data is updated at a predetermined timing.
On the other hand, an image sensor has been proposed (for example, see PTL 3). The image sensor includes a radiation unit, an imaging unit, and a color specification setting unit, in which the radiation unit radiates infrared light having different wavelength intensity distributions to an object, the imaging unit captures an image of the object based on the infrared light having the different wavelength intensity distributions reflected from the object to form image information expressing respective images, and the color specification setting unit sets color specification information for color-specifying the respective images expressed by the formed image information with different monochromes for the image information.